In recent years there has been an exponential increase in demand for wireless communication devices, which was initiated by the development of cellular telephones. Many new applications have been developed that use wireless devices for transmitting digital data. These applications include communications services such as electronic mail and text paging, wireless World Wide Web access, and wireless file transfer, etc. The use of digitally modulated radio signals, e.g. code division multiple access (CDMA), for packetized data transfer has generated a demand for faster transfer rates.
Digitally modulated radio signals are subject to degraded signal quality as a result of: multipath fading caused by reflections from environmental structures such as hilly terrain and/or buildings; doppler effects resulting from movement of mobile communications devices; channel interference; and background noise corruption. Multipath fading and doppler effects cause inter-symbol interference (ISI) which can undesirably affect performance during data transfer. Channel interference in which signals transmitted on one channel (carrier frequency) are detected as noise on other channels, results in similar degradation of data transfer performance. In extreme cases, a bit-error rate (BER) of a digital communications link can reach levels that are outside the permitted tolerance for acceptable or useful data communications.
Various methods have been proposed for maximizing the performance of wireless communications networks. For example, it is known to reduce channel interference by adjusting the transmission power of base stations and wireless terminals of the network. Conventional power control techniques typically adjust wireless terminal transmission powers based on a determination of the mean or average of the interference level detected at a base station. Examples of such power control techniques are provided by J. Zander, in “Distributed Cochannel Interference Control in Cellular Radio Systems,” IEEE Trans. Vehic. Tech., b. 41 (3), pp. 305-311 (August 1992); by G. J. Foschini et al., in “A Simple Distributed Autonomous Power Control Algorithm and Its Convergence,” IEEE Trans. Vehic. Tech., v. 42 (4), pp. 641-646 (November 1993); by A. J. Viterbi, in “CDMA-Principles of Spread Spectrum Communication,” ch. 4.7, pp. 113-119 (Addison-Wesley Pub. Co. 1995); by S. V. Hardy, in “An Algorithm for Combined Cell-Site Selection and Power Control to Maximize Cellular Spread Spectrum Capacity,” IEEE J. Selected Areas in Comm., v. 13, no. 7, pp. 1332-1340 (September 1995); and, by R. D. Yates, in “A Framework for Uplink Power Control in Cellular Radio Systems,” IEEE J. Selected Areas in Comm., v.13, no. 7, pp. 1341-1347 (September 1995). However, the use of the simple mean of the received interference in determining the transmission power often produces a power level that is higher than necessary, causing higher than necessary levels of interference at the base stations. As a result, connection capacity in such systems are still overly limited. U.S. Pat. No. 5,732,328 (which issued to Mitra et al. on Mar. 24, 1998) teaches an alternative method, in which transmission power is controlled on a basis of an information class (i.e. voice, audio or data) of traffic on each link. The method taught by Mitra et al. permits further reductions in transmission power, with corresponding reductions in co-channel interference.
The above examples illustrate ongoing efforts to increase wireless data throughput by reducing channel interference. Each of these systems seek to minimize transmission power on every link, while maintaining acceptable performance in terms of session quality of service requirements on the link in question. Thus if any one or more of carrier-to-interference (C/I) ratio; the signal-to-noise (S/N) ratio; or bit error rate (BER) of any particular link falls outside of an acceptable range, then transmission power on that link is increased. However, that power increase may cause performance reductions on other links due to increased channel interference, while only being effective to recover marginal performance on the link in question. Consequently, conventional methods of reducing channel interference may have an effect of sacrificing data throughput on all links (and thus over-all data through-put) in an effort to maintain marginal data throughput on a small number of poorly-performing links.
Accordingly, a technique for controlling data traffic over a plurality of communications links of a wireless communications network which avoids unnecessarily diminishing overall network data throughput is highly desirable.